Appendicitis is a common acute surgical problem affecting human beings of a wide age range. There are approximately 700,000 cases annually in the United States. A large proportion of cases occur in the 10 to 30 age group. An accurate diagnosis at a sufficiently early stage is a significant factor in achieving a successful outcome.
Many people present to their physician with symptoms suggestive of appendicitis but caused by other ailments such as viral infections. Differentiating the appendicitis patients from those affected with other ailments is a daunting clinical task that physicians face daily. While medical science has an excellent understanding of appendicitis and its treatment, it is very limited in its ability to accurately recognize or diagnose the disease.
Complicating the goal of an accurate and early diagnosis is the considerable overlap of genuine appendicitis with other clinical conditions. There appears to be no individual sign, symptom, test, or procedure capable of providing a reliable indication of appendicitis. Imaging technology is inadequate in identifying and characterizing the appendix, especially in the early stages of the disease when treatment is likely to be most effective. Imaging technology is further handicapped by its expense and its dependence upon the availability of highly trained and experienced people to interpret the studies. This limitation affects thousands of people every year by inaccurately diagnosing their problem or by delaying the accurate diagnosis. In cases of appendicitis, delays in diagnosis are the single most important factor leading to worsening of the condition and more complications related to the disease. The misdiagnosis of appendicitis can lead not only to unnecessary surgery but also to delay of proper therapy for the actual underlying condition.
A dilemma for surgeons is how to minimize the negative appendectomy rate without increasing the incidence of perforation among patients referred for suspected appendicitis. What is desperately needed to more effectively treat this very common ailment is a simple, reliable diagnostic test that is capable of recognizing the earliest stages of the disease process.
The typical pathogenesis in appendicitis begins with obstruction of the lumen, although an initial inflammation of the organ can precede and even contribute to the obstruction. The secreted mucus of the appendix fills the closed lumen, causing an increase in intralumenal pressure and distension. The increased intralumenal pressure can exceed the level of capillary perfusion pressure, resulting in perturbation of normal lymphatic and circulatory drainage. Ultimately the appendix can become ischemic. The appendix mucosa is compromised, which can allow invasion of intralumenal bacteria. In advanced cases, perforation of the appendix may also occur with spillage of pus into the peritoneal cavity.
Currently, the diagnosis of appendicitis is difficult, and the difficulty persists during various stages in the progression of the condition. The following represents a hypothetical portrayal of stages and associated clinical presentations. Artisans of ordinary skill will recognize that a considerable degree of variation will occur in a given patient population.
At the earliest stages of inflammation, a patient can present with a variety of non-specific signs and symptoms. Upon obstruction, presentation can involve periumbilical pain, mild cramping, and loss of appetite. The progress toward increased lumenal pressure and distension can be associated with presentation involving the localization of pain to the right lower quadrant of the abdomen, nausea, vomiting, diarrhea, and low grade fever. If perforation occurs, a patient can present with severe pain and high fever. At this very advanced stage, sepsis can be a serious risk with a potentially fatal outcome.
Practitioners currently use several tools to aid in appendicitis diagnosis. These tools include physical examination, laboratory tests, and other procedures. Routine laboratory tests include complete blood count (CBC) with or without differential and urinalysis (UA). Other tests include a computed tomography (CT) scan of the abdomen and abdominal ultrasonography. Procedures can include, for example, laparoscopic examination and exploratory surgery.
Flum et al. attempted to determine whether the frequency of misdiagnosis preceding appendectomy has decreased with increased availability of certain techniques (Flum D R et al., 2001). These techniques included computed tomography (CT), ultrasonography, and laparoscopy, which have been suggested for patients presenting with equivocal signs of appendicitis. Flum et al. concluded as follows: “Contrary to expectation, the frequency of misdiagnosis leading to unnecessary appendectomy has not changed with the introduction of computed tomography, ultrasonography, and laparoscopy, nor has the frequency of perforation decreased. These data suggest that on a population level, diagnosis of appendicitis has not improved with the availability of advanced diagnostic testing.” The rate of misdiagnosis of appendicitis is about 9 percent in men and about 23.2 percent in women (Neary, W., 2001).
Myeloid-related Protein Complex 8/14 (MRP-8/14) is a heterodimeric complex associated with acute inflammatory conditions (for review see Striz and Trebichavsky, 2004). The complex belongs to the S100 superfamily of proteins and is also referred to S100A8/9, L1, macrophage inhibitory related protein and calprotectin. The heterodimer consists of an 8 kilodalton (MRP-8) and 14 kilodalton (MRP-14) subunit. MRP-8 and MRP-14 are alternatively named S100A8/calgranulin and S100A9/calgranulin b, respectively. MRP-8/14 is a calcium binding protein originally discovered in macrophages. Neutrophils expressing high concentrations of MRP-8/14 are found in a variety of inflammatory conditions, including rheumatoid arthritis, inflammatory bowel disease and allograft rejections (Frosch et al., 2000; Limburg et al., 2000; Burkhardt et al., 2001).
MRP-8/14 is not always diagnostic of inflammation. For example, it does not reliably indicate the presence of inflammatory diverticuli (Gasché, C. 2005). Lymphocytes do not generally contain MRP-8/14 (Hycult Biotechnology, Monoclonal Antibody to Human S100A8/A9), and therefore MRP-8/14 is not diagnostic of inflammation characterized by the presence of lymphocytes but not neutrophils. Also, this protein is not always associated with opportunistic infections (Froland, M. F., et al., 1994).
Haptoglobin is an acute phase protein that binds free hemoglobin following hemolysis. The haptoglobin-hemoglobin complex is removed by the liver. Haptoglobin is a heterotetramer composed of two alpha and two beta subunits. The alpha and beta units are derived from a single polypeptide chain precursor that is enzymatically cleaved to produce the subunits. The molecular weights of the subunits are approximately 9 kd-18 kd and 38 kd for alpha and beta, respectively.
In addition to being a hemoglobin scavenger, haptoglobin has a wide range of biological functions (Dobryszycka, 1997). Haptoglobin has been shown to be upregulated and modulate the immune response in certain infection and inflammatory conditions perhaps by regulating monocyte function (Arredouani et al., 2005). The alpha subunit has been demonstrated to be a potentially useful serum marker for ovarian cancer (Ye et al., 2003).
The ability to accurately diagnose appendicitis would be greatly augmented by the identification of molecules differentially associated with appendicitis.